Merge pull request #57986 from Calinou/doc-geometryinstance3d-transparency

doc/classes/GeometryInstance3D.xml

@@ -57,7 +57,9 @@
 			If a material is assigned to this property, it will be used instead of any material set in any material slot of the mesh.
 		</member>
 		<member name="transparency" type="float" setter="set_transparency" getter="get_transparency" default="0.0">
-			Transparency applied to the whole geometry. In spatial shaders, transparency is set as the default value of the [code]ALPHA[/code] built-in.
+			The transparency applied to the whole geometry (as a multiplier of the materials' existing transparency). [code]0.0[/code] is fully opaque, while [code]1.0[/code] is fully transparent. Values greater than [code]0.0[/code] (exclusive) will force the geometry's materials to go through the transparent pipeline, which is slower to render and can exhibit rendering issues due to incorrect transparency sorting. However, unlike using a transparent material, setting [member transparency] to a value greater than [code]0.0[/code] (exclusive) will [i]not[/i] disable shadow rendering.
+			In spatial shaders, [code]1.0 - transparency[/code] is set as the default value of the [code]ALPHA[/code] built-in.
+			[b]Note:[/b] [member transparency] is clamped between [code]0.0[/code] and [code]1.0[/code], so this property cannot be used to make transparent materials more opaque than they originally are.
 		</member>
 		<member name="visibility_range_begin" type="float" setter="set_visibility_range_begin" getter="get_visibility_range_begin" default="0.0">
 			Starting distance from which the GeometryInstance3D will be visible, taking [member visibility_range_begin_margin] into account as well. The default value of 0 is used to disable the range check.

doc/classes/RenderingServer.xml

@@ -1455,6 +1455,9 @@
 			<argument index="1" name="transparency" type="float" />
 			<description>
 				Sets the transparency for the given geometry instance. Equivalent to [member GeometryInstance3D.transparency].
+				A transparency of [code]0.0[/code] is fully opaque, while [code]1.0[/code] is fully transparent. Values greater than [code]0.0[/code] (exclusive) will force the geometry's materials to go through the transparent pipeline, which is slower to render and can exhibit rendering issues due to incorrect transparency sorting. However, unlike using a transparent material, setting [code]transparency[/code] to a value greater than [code]0.0[/code] (exclusive) will [i]not[/i] disable shadow rendering.
+				In spatial shaders, [code]1.0 - transparency[/code] is set as the default value of the [code]ALPHA[/code] built-in.
+				[b]Note:[/b] [code]transparency[/code] is clamped between [code]0.0[/code] and [code]1.0[/code], so this property cannot be used to make transparent materials more opaque than they originally are.
 			</description>
 		</method>
 		<method name="instance_geometry_set_visibility_range">